title: Cadmium retention in rice roots is influenced by cadmium availability, chelation and translocation.
abstract: Analysis of rice plants exposed to a broad range of relatively low and environmentally realistic Cd concentrations showed that the root capacity to retain Cd ions rose from 49 to 79%, corresponding to increases in the external Cd²+ concentration in the 0.01-1 µM range. Fractioning of Cd ions retained by roots revealed that different events along the metal sequestration pathway (i.e. chelation by thiols, vacuolar compartmentalization, adsorption) contributed to Cd immobilization in the roots. However, large amounts of Cd ions (around 24% of the total amount) predictable as potentially mobile were still found in all conditions, while the amount of Cd ions loaded in the xylem seemed to have already reached saturation at 0.1 µM Cd²+, suggesting that Cd translocation may also play an indirect role in determining Cd root retention, especially at the highest external concentrations. In silico search and preliminary analyses in yeast suggest OsHMA2 as a good candidate for the control of Cd xylem loading in rice. Taken as a whole, data indicate Cd chelation, compartmentalization, adsorption and translocation processes as components of a complex 'firewall system' which acts in limiting Cd translocation from the root to the shoot and which reaches different equilibrium positions depending on Cd external concentration.
authors.affiliation: Dipartimento di Produzione Vegetale, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: Fabio Francesco
authors.initials: FF
authors.lastname: Nocito
authors.affiliation: Dipartimento di Produzione Vegetale, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Lancilli
authors.affiliation: Dipartimento di Produzione Vegetale, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: Bianca
authors.initials: B
authors.lastname: Dendena
authors.affiliation: Dipartimento di Produzione Vegetale, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Lucchini
authors.affiliation: Dipartimento di Produzione Vegetale, Università degli Studi di Milano, 20133 Milan, Italy.
authors.forename: Gian Attilio
authors.initials: GA
authors.lastname: Sacchi
mesh_terms: D001692:Biological Transport; D002104:Cadmium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002614:Chelating Agents / Q000378:metabolism*; D002850:Chromatography, Gel; D018506:Gene Expression Regulation, Plant; D005978:Glutathione / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D018520:Plant Shoots / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D002614:Chelating Agents; D010940:Plant Proteins; D013438:Sulfhydryl Compounds; D002104:Cadmium; D005978:Glutathione